The present invention relates to a semiconductor device having a tungsten nitride film containing fluorine (WNF film).
Recently, there is a great demand for a highly reliable multilayer wiring technique capable of forming via holes, contact holes or fine wires, which have high aspect ratios, so as to achieve a high integration of LSI. For example, conventionally, chemical vapor deposition methods have been proposed as a technique for burying a wire having a high aspect ratio, a typical one of which is blanket W-CVD using tungsten hexafluoride (WF.sub.6) and hydrogen (H.sub.2).
However, with the blanket W-CVD, a good adhesion with respect to the underlayer of Si or oxide film, cannot be obtained, and therefore it is required to provide a metal adhesion layer such as of titanium nitride, tantalum nitride (TaN), tungsten titanium or tungsten nitride, between the underlayer and W. Conventionally, such a metal adhesion layer is formed by the sputtering or reactive sputtering technique; however it is preferable that a CVD method having a high step coverage should be employed when applied to fine via holes or contact holes.
Further, conventionally, for wires made of low-resistance materials such as Al and Cu, a metal adhesion layer made of, typically, TiN is used as a diffusion barrier; however recently there is an increasing demand for a CVD method having a high step coverage, as the size of the wiring portion becomes finer.
In the case where a TiN film is formed by the CVD method, the film is formed with use of titanium chloride (TiCl.sub.4) and ammonium (NH.sub.3); however these materials cannot be used after the formation of the aluminum wire since the temperature for the formation of the film is as high as 600.degree. C. or higher. Further, chlorine remains as residue in the film, and therefore the corrosion of the wire easily occurs. Furthermore, the formation of a TiN film with use of a Ti-based organic metal gas and ammonium is presently studied; however it entails the problem of an increase in resistance, caused by impurities or moisture absorption, and therefore has not yet been established as a film forming method.
As described, the formation of a TiN, TaN or TiW film with use of the CVD method, entails a number of drawbacks to be solved.
In the meantime, the formation of tungsten nitride film containing fluorine (WNF film), using material gases of WF.sub.6 and NH.sub.3, is also studied. The WNF film is thermally stable, and it can be formed at a low substrate temperature of 600.degree. C. or less by a vacuum CVD method. Therefore, the use of the film as an adhesion layer for Mo, or a barrier layer for an Al or Cu wire is studied.
However, the WNF film made by the conventional vacuum CVD method using WF.sub.6 and NH.sub.3, entails the problems of a poor step coverage and a high film stress. One of the factors which create such problems is considered that the content of fluorine in the WNF film is low. Therefore, the WNF film made by the conventional vacuum CVD method using WF.sub.6 and NH.sub.3, should not be appropriate as an adhesion layer, barrier layer or the like, in a fine hole.